We want to know which of two types of filters should be used. A test was designed in which the strength of a signal could be varied from zero to the point where the operator first detects the image. At that point, the intensity setting is recorded. Lower settings are better. Twenty operators were asked to make one reading for each filter.

Assuming the intensity readings are normally distributed, estimate the mean difference between the two readings using a 90% confidence interval.

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Operator 1 2 3 45 6 7 8 9 10 Filter l Filter2 92 84 92 90 93 9 92 90 93 90 96 83 97 93 99 95 97 91 100 92 Operator 11 12 13 14 15 16 17 18 19 20 Filter Filter2 88 89 86 91 89 90 90 80 80 90 88 8985 94 90 92 91 78 77 93